The proposed study will be the largest and first truly longitudinal study focused on examining the risk of adverse driving outcomes throughout adolescence and young adulthood (age 16-25) among a general population of children diagnosed with Attention-Deficit/Hyperactivity Disorder (ADHD). ADHD is one of the most common childhood disorders. For the majority of affected children, the defining symptoms of ADHD- inattention, hyperactivity, and impulsivity-persist into adolescence, a time at which many likely get licensed to drive. Motor vehicle crashes are the leading cause of death and disability among adolescents with inattention/distraction and unsafe driving behaviors major causes-creating the potential for heightened adverse health risk for adolescents with ADHD. Small studies among more severely-affected adolescents and young adults suggest an increased risk of adverse driving outcomes. However, these studies have significant methodological limitations and were mostly conducted prior to the year 2000, when distractions from electronic devices were less prevalent and before Graduated Driver Licensing systems-which restrict novice young drivers' exposure to hazardous conditions-were widely implemented. We still know little about when adolescents with ADHD get licensed, whether they engage in unsafe driving behaviors (e.g., speeding, reckless driving, seat belt nonuse) more often than other adolescents, and the specific mechanisms by which ADHD influences crash risk. This crucial study will provide the evidence base needed to inform medical, behavioral, technological, and policy interventions targeted to novice drivers with ADHD. The study aims to: compare licensing trajectories of adolescents with and without ADHD; examine the effect of ADHD on the risk of citations and crashes, and further determine the role of inattention/distraction and unsafe driving behaviors in these crashes; and determine whether the effect of ADHD varies by gender, age, driving experience, and diagnosis with a comorbid mental health condition (i.e., disruptive behavior, anxiety, or mood disorder). Further, it will be the first observational study to examine the association between long-term ADHD medication use and driving outcomes among adolescents with ADHD. Two unique and rich data sources will be combined: (1) electronic health record information for over 1,600 children with ADHD and 10,000 children without ADHD who were born between 1987-1995 and who were patients of The Children's Hospital of Philadelphia's New Jersey (NJ) primary care network; and (2) a linked database that contains the full licensing, citation, and crash history of every NJ driver through December 2013. The study will support our long-term goal of developing interventions that tailor the licensing and learning-to-drive process to, and ensure safe driving behaviors among, teens with ADHD. It will also be the first study to link children's medical records to their future outcomes as young drivers-a methodological advancement in the field of young driver research that will provide a novel method to investigate the effect of other medical conditions/events on traffic outcomes.